Prabbaly either the Person you are trying to sell it to dosent want it. EX. If you Try to Sell a Sword at a Mages staff place the sword wont appear. Try and sell the stuff at certen places. Like Swords and other meele weps sell at the Weps shop or armor shop. and Item like potions at a ingreadents shop or mages shop. Stuff like that OR the stuff you are trying to sell is stolen. And to see if somthing is stolen there will be a Red Hand icon near the picture of the Item